Chemistry - Hydrocarbon Question with Solution | TestHub

Question Explanation:

We are asked to compare the rate of acid-catalyzed hydration of different styrene derivatives.

Concept :

This question is based on Electrophilic addition of H₃O⁺ to alkenes, Carbocation stability, Resonance effects, Electron-donating vs electron-withdrawing substituents.

Solution :

Alkene + H₃O⁺ → carbocation intermediate → OH⁻ adds → alcohol.

Rate depends on the stability of carbocation formed.

Electron-donating groups increase rate.

Electron-withdrawing groups decrease rate.

(I) Styrene (Ph–CH=CH₂ ): carbocation formed is benzylic → resonance stabilized.

(II) p-Hydroxy styrene (p-OH–C₆H₄–CH=CH₂ ): –OH is electron-donating via resonance → stabilizes carbocation more → rate increases.

(III) p-Nitro styrene (p-NO₂–C₆H₄–CH=CH₂ ): –NO₂ is strongly electron-withdrawing → destabilizes carbocation → rate decreases.

(IV) p-Methyl styrene (p-CH₃–C₆H₄–CH=CH₂): –CH₃ is weakly electron-donating → slightly stabilizes carbocation → rate slightly higher than styrene.

Final answer : Option(C)